As sea temperatures have risen in recent decades, enormous sheets of a mucus-like material have begun forming more often, oozing into new regions, and lasting longer, a new Mediterranean Sea study says (sea "mucus" blob pictures).

And the blobs may be more than just unpleasant.

Up to 124 miles (200 kilometers) long, the mucilages appear naturally, usually near Mediterranean coasts in summer. The season's warm weather makes seawater more stable, which facilitates the bonding of the organic matter that makes up the blobs (Mediterranean map).

Now, due to warmer temperatures, the mucilages are forming in winter too—and lasting for months.

Until now, the light-brown "mucus" was seen as mostly a nuisance, clogging fishing nets and covering swimmers with a sticky gel—newspapers from the 1800s show beach-goers holding their noses, according to study leader Roberto Danovaro, director of the marine science department at the Polytechnic University of Marche in Italy.

But the new study found that Mediterranean mucilages harbor bacteria and viruses, including potentially deadly E. coli, Danovaro said. Those pathogens threaten human swimmers as well as fish and other sea creatures, according to the report, published September 16 in the journal PloS One.

Blobs Born of "Marine Snow"

A mucilage begins as "marine snow": clusters of mostly microscopic dead and living organic matter, including some life-forms visible to the naked eye—small crustaceans such as shrimp and copepods (copepod picture), for example.

Over time, the snow picks up other tiny hitchhikers, looking for a meal or safety in numbers, and may grow into a mucilage.

The blobs were first identified in 1729 in the Mediterranean, where they're most often seen. The sea's relative stillness and shallowness make the water column more stable, providing ideal conditions for mucilage formation.